Process for the manufacture of the gamma isomer of hexachlorocyclohexane



Patented Nov. 6, 1951 PROCESS FOR THE MANUFACTURE OF THE GAMIWA ISOMER OF HEXACHLOROCYCLO- HEXANE Harry Bender and Harold M. Pitt, Torrance, Calif., assignors to Stanfler Chemical Company, a corporation of California No Drawing. Application October 28,1949, Serial No. 124,231

Claims.

This is a continuation-in-part of our application Serial No. 73,872, filed January 31, 1949, now abandoned.

This invention relates to the manufacture of hexachlorocyclohexane and, more particularly, to the production of hexachlorocyclohexane in which the gamma isomer has been selectively increased to a desired extent.

1f benzene is reacted with chlorine under conditions promoting the addition of chlorine but not the substitution of chlorine for hydrogen, a mixture results of the isomers of hexachlorocyclohexane. So far, five isomers have been identified, the alpha, beta, gamma, delta, and epsilon. It has been recognized heretofore that materials containing the gamma isomer or hexachlorocyclohexane are active insecticides and are useful as pest control materials. For various applications, it is desired to increase the content of the gamma isomer above that concentration in which the gamma isomer is generally produced by the chlorination operation, e. g., usually 6% to 12%; in some instances, it is even desired to produce relatively pure gamma isomer of hexachlorocyclohexane.

According to the present invention, a process is provided for treating crude hexachlorocyclohexane to obtain the substantially pure gamma isomer.

We have found that the presence of the delta isomer interferes with the gamma isomer crystalhexachlorocyclohexane solution so viscous as to interfere with and reduce the rate of growth of gamma isomer crystals. For these reasons, it is generally essential first to extract the crude hexachlorocyclohexane with a solvent for the delta isomer, and we have used an aliphatic alcohol such as methyl alcohol, ethyl alcohol, normal propyl alcohol, or isopropyl alcohol to remove the delta isomer as well'as various impurities which carry overfrom the benzene when this is not of very great purity. Only sufilcient ofthe solvent should be used as is necessary to remove the, delta isomer and impurities to avoid loss of the valuable gamma isomer. isopropyl alcohol is the preferred solvent, for it has the greatest solubility ratio as between the delta isomer and the gamma isomer.

As illustrative of practice of the present invention, crude 'hexachlorocyclohexane, produced in any desired manner and containing a useful concentration of the gamma isomer, is freed of the largely of the gamma and alpha isomer. This material is then extracted with isopropyl alcohol at a,moderately elevated temperature; the alcohol extract is then separated from the remaining undissolved solid and is cooled to a tempera ture whereat the gamma isomer crystallizes; the alcohol, saturated with alpha isomer, is separated from the crystals and returned to extract more of the starting material. in the absence of the delta isomer, between a temperature of 30 C. and 465 C., the solubility of the gamma isomer in isopropyl alcohol is increased by the presence of the alpha isomer; that below 30 C., the solubility of the gamma isomer is lowered by the presence of the alpha isomer; and that above 465 C., the solubility oi the gamma isomer is lowered by the presence of the alpha isomer. Stated otherwise, at 30 C. and at 46.5" C., the solubilities of the gamma isomer in isopropyl alcohol are the same whether the alpha isomer is present or not; between these temperatures, the solubility of the gamma isomer is increased by the presence of the alpha isomer over that of the gamma isomer in the absence of the alpha isomer; above about 50 C., the solubility of the gamma isomer is lowered while that of the alpha isomer is increased when both are present in isopropyl alcohol. It is therefore preferred to make the extraction with the isopropyl alcohol at a temperature of about 47 C., and generally between 45 and 50 C. to dissolve a maximum quantity of the gamma isomer and to then cool this liquid to below about 30 C. to crystallize the gamma isomer; the gamma isomer has less tendency to supersaturate than does the alpha isomer so that the gamma isomer crystallizes first and it is not necessary to cool to a temperature requiring mechanical refrigeration since one can secure substantially the same weight crop of gamma isomer by permitting the crystallization to continue for a slightly longer period of time at a temperature attained by atmospheric cooling or with water cooled in a cooling tower; the use of such a longer time period is feasible because of the tendency of the alpha isomer to supersaturate to a greater relative extent than the gamma isomer. The upper temperature of 47 C. can be exceeded somewhat since the effect on the alpha isomer solubility is not too adverse and one can work successfully in the range of 45 to 50 C. Similarly, at the lower temperature one can work successfully at 30 C. and at temperatures below this down to 15 C. and even lower, depending upon the refrigeration or cooldelta isomer to provide a material consisting s5 ingavailable.

We have found that,

To make the extraction requires from fifteen pounds at 50 C. to ten pounds at 45 C. of isopropyl alcohol per pound of gamma isomer present. It is preferred to employ a minimum of solvent to avoid solution of the beta isomer and we therefore prefer to employ quantities slightly less than these, jg'., 13.6 poundsat 45 and 11.3 pounds at 50 Cjper pound oi! gamma isomer present in the isomer mixture undergoing extraction and to wash the cake free of adhering mother liquor, the'wash liquor being used for delta isomer, separation. If enough solvent is employedinitially to dissolve all of the mixture, then an' uneconomically large quantity of the gamma isomer will remain in the solution following the gamma isomer crystallization.

As an example of practice of the invention, the following is set forth by way of illustration:

Benzene was chlorinated by addition to produce hexachlorocyclohexane in benzene solution which was evaporated partially and then cooled to precipitate alpha and beta isomers. The remaining'solution was then evaporated to dryness; it contained 25% of the gamma isomer.

100 pounds of the 25% gamma isomer material was mixed at 75 with 43 pounds of anhydrous isopropyl alcohol to form a thin slurry which was allowed to cool to 25 with slow agitation to dissolve the delta isomers and any impurities. The slurry was then filtered and the cake washed with three gallons of cold isopropyl alcohol to remove delta isomer traces. The wash liquor was kept separate and used as part of the liquor for the next batch. The moist cake on the filter contained the recoverable gamma, in this case 17.5 pounds, or 70% of the original 25 pounds.

The cake was removed from the filter and extracted at 50 C. with fresh isopropyl alcohol for the first batch. At 50 C. each pound of gamma about 75 C. and with sumcient solvent to effect solution of substantially all of the alpha and gamma isomers present; cold mixing or use of insufficient solvent will leave the delta isomer and impurities locked up in the interior of lumps and agglomerates of the crude material when the solution is cooled and the gamma and alpha isomers crystallize; the solution should be agitated vigorously during the cooling to ensure that the alpha and gamma isomers form only small crystals for agglomerates or large crystals will entrain delta isomer or impurities.

We claim:

1. A process for treating crude hexachlorohexane, obtained by the addition chlorination of benzene, to obtain a fraction containing an enhanced proportion of the gamma isomer comprising dissolving the crude hexachlorocyclohexane substantially completely in a lower aliphatic alcohol solvent at a temperature of about 40-100 C., cooling the so-formed solution to about 30 C. and agitating vigorously to form a mixture of small crystals of the alpha and gamma isomers and a solution containing the delta isomer, separating the so-formed crystal mixture from the delta isomer solution, mixing said crystal mixture with from 15 to 10 pounds of isopropyl alcohol per pound of gamma isomer and at a temperature between 45 and 50 C., separating the undissolved solids, cooling the resulting solution to a temperature below about 30 C. to precipitate crystals of the gamma isomer of hexachlorocyclohexane, and separating the gamma isomer crystals from the solution.

in the cake required 11.35 pounds of isopropyl alcohol to effect complete solution; the cake in this example required 11.35 X 17.5 or 199 pounds of the alcohol. The slurry was then filtered at 50 C. The filtrate contained all the gamma isomer plus 7.4'pounds of the alpha isomer. The cake was reject alpha isomer; it was washed with isopropyl alcohol to recover the adhering mother liquor, the wash liquor being thereafter used for delta isomer removal on a fresh batch.

The filtrate was transferred to a crystallizing.

tank where it was heated to the boiling point to dissolve any seeds of alpha or gamma which might have been in the tank or liquor and was then allowed to cool to 20-24 C. to precipitate the gamma! isomer over a period of six hours. It is not us ally necessary to seed the tank with gammaisomer crystals after it has cooled to 40 or below, although this can be done.

The alpha supersaturates as the gamma crystallizes and a crop of 13 pounds of gamma iso mer crystals per 50 gallons has been repeatedly obtained. The theoretical yield is higher than this, but the product will be contaminated with alpha if the entire amount of gamma isomer present is given time to crystallize.

The mother liquor from a crystal crop can be used as part of the solvent for the next extraction until it has picked up too much water from the air or is contaminated with too much of the small amount of delta, etc., which may scape the primary puri 'ation step.

The initial mixing f the crude hex'achlorocyclohexane should at a temperature sufliciently elevated, e. g. 40-1 00 qfpreferably 2. A process as in claim 1 wherein the solvent employed to dissolve the crude hexachlorocyclohexane is isopropyl alcohol.

3. A process for treating crude hex'achlorocyclohexane obtained by the addition chlorination of benzene and which has been freed of delta isomer, to obtain a fraction containing an enhanced proportion of the gamma isomer,-comprising extracting the hexachlorocyclohexane with from 13.6 pounds to 11.3 pounds of isopropyl alcohol per pound of gamma isomer and at a temperature between and C., cooling the resulting solution to a temperature below about 30 C. to precipitate crystals of the gamma isomer of hexachlorocyclohexane, and separating the crystals from the solution.

4. A process for treating crude hexachlorocyclohexane obtained by the addition chlorination of benzene and which has been freed of delta isomer, to obtain a fraction containing an enhanced proportion of the gamma isomer, comprising extracting the hexachlorocyclohexane with from 13.6 pounds to 11.3 pounds of isopropyl alcohol per pound of gamma isomer and at a temperature between 45 and 50 C., cooling the resulting solution to below 30 C. to precipitate crystals of the gamma'isomer of hexachlorocyclohexane and separating the crystals from the solution.

5. A process for extracting selectively the delta and the gamma isomer from crude hexachlorocyclohexan obtained by the addition chlorination of benzene, comprising mixing the said hexachlorocyclohexane with only sufliciefit isopropyl alcohol at about 75 C. to dissolve the delta isomer' present and to form a first slurry, cooling' the slurry, filtering the cooled slurry and recovering the filter cake, mixing said cake at about 45-50 C. with from 15 to 10 pounds of isopropyl alcohol per pound of gamma isomer present to form a second slurry, filtering the seco nd slurry at a temperature of about 50 C. and

recovering the filtrate, heating the filtrate substantially to boiling, cooling, the heated filtrate to a temperature below about 30 C. to crystallize the gamma isomer of hexachlorocyclohexane, and recovering the crystallized gamma isomer.

HARRY BENDER. HAROLD M. PITT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,438,900 Cooke et al Apr. 6, 1948 5 FOREIGN PATENTS Number Country Date 471,941 Belgium Apr. 1947 573,693 Great Britain Dec. 3, 1945 618,994 'Great Britain Mar. 2, 1949 10 OTHER REFERENCES Slade, "Chemistry and Industry, October 13, 1945, pages 314-6. 

1. A PROCESS FOR TREATING CRUDE HEXACHLOROHEXANE, OBTAINED BY THE ADDITION CHLORINATION OF BENZENE, TO OBTAIN A FRACTION CONTAINING AN ENHANCED PROPORTION OF THE GAMMA ISOMER COMPRISING DISSOLVING THE CRUDE HEXACHLOROCYLOHEXANE SUBSTANTIALLY COMPLETELY IN A LOWER ALIPHATIC ALCOHOL SOLVENT AT A TEMPERATURE OF ABOUT 40*-100* C., COOLING THE SO-FORMED SOLUTION TO ABOUT 30* C. AND AGITATING VIGOROUSLY TO FORM A MIXTURE TO SMALL CRYSTALS OF THE ALPHA AND GAMMA ISOMERS AND A SOLUTION CONTAINING THE DELTA ISOMER, SEPARATING THE SO-FORMED CRYSTAL MIXTURE FROM THE DELTA ISOMER SOLUTION, MIXING SAID CRYSTAL MIXTURE WITH FROM 15 TO 10 POUNDS OF ISOPROPYL ALCOHOL PER POUND OF GAMMA ISOMER AND AT A TEMPERATURE 45* AND 50* C., SEPARATING THE UNDISSOLVED SOLIDS, COOLING THE RESULTING SOLUTION TO A TEMPERATURE BELOW ABOUT 30* C. TO PRECIPITATE CRYSTALS OF THE GAMMA ISOMER OF HEXACHLOROCYCLOHEXANE, AND SEPARATING THE GAMMA ISOMER CRYSTALS FROM THE SOLUTION. 